Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309-0347.
Mol Biol Cell. 2018 Jul 15;29(13):1718-1731. doi: 10.1091/mbc.E18-01-0015. Epub 2018 May 23.
Lysosomes are dynamic organelles with critical roles in cellular physiology. The lysosomal signaling lipid phosphatidylinositol 3,5-bisphosphate (PI(3,5)P) is a key regulator that has been implicated to control lysosome ion homeostasis, but the scope of ion transporters targeted by PI(3,5)P and the purpose of this regulation is not well understood. Through an unbiased screen in Saccharomyces cerevisiae, we identified loss-of-function mutations in the vacuolar H-ATPase (V-ATPase) and in Vnx1, a vacuolar monovalent cation/proton antiporter, as suppressor mutations that relieve the growth defects and osmotic swelling of vacuoles (lysosomes) in yeast lacking PI(3,5)P. We observed that depletion of PI(3,5)P synthesis in yeast causes a robust accumulation of multiple cations, most notably an ∼85 mM increase in the cellular concentration of potassium, a critical ion used by cells to regulate osmolarity. The accumulation of potassium and other cations in PI(3,5)P-deficient yeast is relieved by mutations that inactivate Vnx1 or inactivate the V-ATPase and by mutations that increase the activity of a vacuolar cation export channel, Yvc1. Collectively, our data demonstrate that PI(3,5)P signaling orchestrates vacuole/lysosome cation transport to aid cellular osmoregulation.
溶酶体是具有重要细胞生理学功能的动态细胞器。溶酶体信号脂质磷脂酰肌醇 3,5-二磷酸（PI(3,5)P）是一种关键的调节剂，被认为可以控制溶酶体离子稳态，但 PI(3,5)P 靶向的离子转运体的范围和这种调节的目的尚不清楚。通过在酿酒酵母中的无偏筛选，我们鉴定出液泡 H+-ATP 酶（V-ATPase）和液泡单价阳离子/质子反向转运蛋白 Vnx1 的功能丧失突变是抑制突变，可缓解缺乏 PI(3,5)P 的酵母中液泡（溶酶体）的生长缺陷和渗透肿胀。我们观察到 PI(3,5)P 合成的耗尽会导致多种阳离子的大量积累，尤其是细胞内钾浓度增加约 85 mM，钾是细胞用于调节渗透压的关键离子。在缺乏 PI(3,5)P 的酵母中，通过使 Vnx1 失活或使 V-ATPase 失活，以及通过增加液泡阳离子出口通道 Yvc1 的活性的突变，可以缓解钾和其他阳离子的积累。总的来说，我们的数据表明 PI(3,5)P 信号协调溶酶体阳离子转运以帮助细胞渗透压调节。
